Millennial-scale iron fertilization of the eastern equatorial Pacific over the past 100,000 years

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Abstract

The eastern equatorial Pacific Ocean plays a crucial role in global climate, as it is a substantial source of CO2 to the atmosphere and accounts for a significant portion of global new export productivity. Here we present a 100,000-year sediment core from the eastern equatorial Pacific, and reconstruct dust flux, export productivity and bottom-water oxygenation using excess-230Th-derived fluxes of 232Th and barium, and authigenic uranium concentrations, respectively. We find that during the last glacial period (71,000 to 41,000 years ago), increased delivery of dust to the eastern equatorial Pacific was coeval with North Atlantic Heinrich stadial events. Millennial-scale pulses of increased dust flux coincided with episodes of heightened biological productivity, suggesting that dissolution of dust released iron that promoted ocean fertilization. We also find that periods of low atmospheric CO2 concentrations were associated with suboxic conditions and increased storage of respired carbon in the deep eastern equatorial Pacific. Increases in CO2 concentrations during the deglaciation are coincident with increases in deep Pacific and Southern Ocean water oxygenation levels. We suggest that deep-ocean ventilation was a primary control on CO2 outgassing in this region, with superimposed pulses of high productivity providing a negative feedback.

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Figure 1: Site locations and seasonal ITCZ migration.
Figure 2: Palaeoclimatic reconstructions in EEP marine sediment cores compared with the NGRIP record.
Figure 3: Palaeoclimatic reconstructions in EEP marine sediment core 17JC compared with ice core records.
Figure 4: Atmospheric CO2, bottom-water oxygenation and EEP oceanic pCO2 over the past 25 kyr.

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Acknowledgements

This research was funded by NSF grant OCE-0851056 to F.M. and M.L. Additional financial support was provided to F.M. by the Jane and R. Ken Williams Chair in Ocean Drilling Science, Technology, and Education. We thank L. Romero for her technical assistance in the laboratory. We thank A. Erhardt for constructive review.

Author information

M.R.L. and F.M. designed the study. M.R.L. sampled the core, and performed the U–Th isotope analyses. M.R.L. and M.M.W. performed the Ba analyses. M.R.L. separated the foraminifera for oxygen-isotope analysis. M.R.L. and J.E.H. separated the foraminifera for radiocarbon analysis. All authors contributed to interpretation of the data. M.R.L. and F.M. wrote the manuscript, and all authors provided comments and revisions.

Correspondence to Franco Marcantonio.

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Loveley, M., Marcantonio, F., Wisler, M. et al. Millennial-scale iron fertilization of the eastern equatorial Pacific over the past 100,000 years. Nature Geosci 10, 760–764 (2017) doi:10.1038/ngeo3024

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